Created attachment 1892590 [details]
Video showing that the German keyboard stays active even after switching to table:cangjie5

[mfabian@fedora ~]$ cat /etc/fedora-release 
Fedora release 36 (Thirty Six)
[mfabian@fedora ~]$ rpm -q ibus
ibus-1.5.26-10.fc36.x86_64
[mfabian@fedora ~]$ rpm -q plasma-desktop
plasma-desktop-5.24.5-1.fc36.x86_64
[mfabian@fedora ~]$ 

Some ibus input methods need to enforce a certain keyboard layout. For example table:cangjie5 needs to enforce the 'us' layout: 

[mfabian@fedora ~]$ /usr/libexec/ibus-engine-table --xml | grep -A 6 'name>table:cangjie5'
        <name>table:cangjie5</name>
        <longname>CangJie5</longname>
        <language>zh</language>
        <license>Freely redistributable without restriction</license>
        <author>chinesecj.com (倉頡之友‧馬來西亞)</author>
        <icon>/usr/share/ibus-table/icons/cangjie5.svg</icon>
        <layout>us</layout>
[mfabian@fedora ~]$ 

On Plasma Wayland, ibus cannot do this. 

In the attached video, I switch to the  German keyboard layout using the KDE keyboard switcher (the keyboards in the ibus menu are hidden except for "No input method"),

Then I switch to table:cangjie5 using the ibus menu, the keyboard is not switched to 'us': When typing the key labelled 'y' on the us layout, followed by Return, the character 'z' is committed. This shows that the German layout is still used as the German layout has a 'z' at this key position.